In the fabrication of a semiconductor device, the cleaning technique of a semiconductor wafer becomes important. A conventional wet treatment apparatus for the semiconductor wafer, used for cleaning the semiconductor wafer, has employed an overflowing method. The wafer is introduced into a processing tank constructed in a manner that a processing solution (such as cleaning water) is introduced from its bottom and the level thereof raised until the wafer is submerged to thereby wet-treat the wafer.
FIG. 1 is a perspective view showing a conventional wet treatment apparatus for a semiconductor wafer, FIG. 2 is a cross-sectional view taken along line A-A' of FIG. 1, and FIG. 3 is a cross-sectional view taken along line B-B' of FIG. 1. As shown in FIGS. 1, 2 and 3, the conventional apparatus includes a processing tank 11 constructed in a manner that a processing solution supply line 12 is connected to its bottom 11-1, to supply a processing solution (such as cleaning water or a cleaning solution) into the processing tank 11, and the supplied processing solution overflows its side wall 11-2. The semiconductor wafer 10 is introduced into processing tank 11.
Generally, a plurality of semiconductor wafers 10 are carried in a wafer carrier 15 and introduced into the processing tank 11. A discharge ditch 14 is formed around side wall 11-2 of the processing tank 11, and its bottom is connected to a discharge line 13. Discharge line 13 is connected to processing solution supply line 12 through a pump 16 and filter 17, to purify the discharged processing solution through filter 17. By doing so, the discharged processing solution is recirculated.
There is a conventional wet treatment apparatus having a structure in which its discharge line and supply line are not connected to each other, and the processing solution discharged from the discharge line is discarded. This apparatus is used in case that the processing solution which passes through its processing tank is severely contaminated.
Reference numeral 18 designates a flow control board in which holes are formed, probably formed uniformly, to make the processing solution flow into each portion of processing tank 11. Accordingly, when wafer carrier 15 containing the plurality of wafers 10 is introduced into the conventional processing tank 11, the processing solution (such as cleaning water) supplied through supply line 12 flows inside processing tank 11, to wet-treat the wafer. Then, the processing solution overflows side wall 11-2 of the processing tank 11, to be introduced into the discharge ditch. The processing solution introduced into discharge ditch 14 is discharged through discharge line 13, to be recirculated through filter 17 by the pump 16.
The aforementioned conventional apparatus is disclosed on page 94 of the publication entitled, "24th Symposium on ULSI Ultra Clean Technology," Japan, Mar. 7-8, 1995, and in U.S. Pat. No. 5,370,142.
As shown in FIGS. 1, 2 and 3, in the conventional apparatus, the inner sides of processing tank side walls 11-2 make a right angle with each other, or the inner side of side wall 11-2 and inner side of bottom 11-1 meet at right angles to form a corner portion. By doing so, contamination material (such as particles or residue) is stuck in the corner, and serves as a contamination source. This contaminates the processing solution and wafer.
As shown in FIG. 3, in the above-described conventional apparatus, sharp protrusion portions 19a and 19b are formed on portions where processing tank 11 and processing solution supply line 12 meet, and discharge ditch 14 and discharge line 13 meet. Abrasion, due to the processing solution flowing past, occurs at these points of protrusion, increasing the generation of contamination material in the processing tank 11. In case that the processing solution is purified through filter 17 to be recirculated, the increase of contamination material in the processing tank 11 reduces the durability of filter 17.